Method of producing a sterile meat package



METHOD OF PRODUCING A STERILE MEAT PACKAGE Application December 20, 1952, Serial No. 327,176

1 Claim. (Cl. 99-174) N Drawing.

' The present invention relates to the art of food sterilization and preservation by ionizing penetrating radiation such as highvelocity electrons, for instance.

One of the objects of our invention is to use ionizing penetrating radiation, such as high voltage, high intensity electrons for instance, of limited penetrating range, for the preservation of foodstufis to be sold in packages of such dimensions as to place a portion of the substance beyond the range of penetration of the electrons.

Yet another object is to provide a novel package for food substances to be sterilized by ionizing penetrating radiation which is well adapted to the capabilities of such sterilization processes when conducted at relatively low cost with low voltage equipment.

Still another object is to provide a novel package or packaging method to be used in conjunction with sterilization by penetrating ionizing radiation which renders such sterilization processes more efficient.

Other objects and advantages will become apparent from the following description of a preferred embodiment of our invention.

Processes are now known for the sterilization of food and other substances which involve bombarding the substance with high velocity electrons having sufficient velocityto pass through the substance, or, in the alternative, to completely penetrate the substance when it is bombarded from opposite sides so as to destroy the capability of propagation of microorganisms present in the substance. For instance such a process is disclosed in Reissue Patent No. 23,195.

There are instances, however, where it will be desired to use penetrating ionizing radiation of comparatively low voltage for the'purpose of producing sterility in certain food substances to be sold in packages larger than can be penetrated completely by the equipment available.

In the interest of better understanding theprocess of paper or the like can be used. It is preferred that after' the meat substance has been placed within the package that the package be heat sealed if the package material permits this. This can be accomplished in production in an economical fashion by applying well known techniques.

These individual packages of meat enclosed within the plastic or other bags, are then pressed flat so as to have a relatively uniform predetermined thickness which is within the penetrating range of the radiation source available, or, if desired, the equipment can be so arranged as to bombard the packages from opposite sides thereby enabling thicker packages to be used.

After the packages have been subjected to electron bombardment or to other penetrating radiation having the capability of causing sufiicient ionization within the substance to produce sterility, the individual packages are shaped to fit the particular container or box in which the meat substance or other food is to be marketed. For instance, the irradiated thin, plastic enclosed packages of meat can be rolled or pressed to cylindrical form to fit an ordinary tin coated sheet steel can, or, if desired, these pliable packages can be folded or otherwise shaped to a generally rectangular form so as to fit any suitable cardboard carton. Of course, two or more individual thin sterilized packages of food can be shaped so that together they fill one larger can or carton. p

A specific variant of the above generally described process follows:

Fifty pounds or so of ground meat is taken from a cooler and is preferably deaerated and then stuffed into a tube of laminated cellophane of six-inch Width. This protecting film is bacteria-proof and is substantially proof against passage of moisture and gas.

After packing, one end of the tube is heat sealed (this of course may be done before stufling) while through the open end of the tube the contents is deaerated by ordinary vacuum technique, and the vacuum finallyis replaced by oxygen free nitrogen.

The open end of the tube is then hermetically sealed, and the tube and contents are feed through cooled rollers so as to form a ribbon about six inches wide and twelve the present invention will be described in conjunction V with the preservation and packaging of a specific food substance- -ground meat. ever, that the same method or minor variations thereof will apply equally well to the preservation of other substances. I

As a starting point in explaining the process it will be assumed that it is desired to sterilize ground meat by electron bombardment and sell the sterilized product in packages which have dimensions of such order that the center of the package of meat is beyond the range of penetration of high velocity electrons available from a particular electron accelerator. According to the present invention, the necessary quantity of meat to be packaged within the container is sealed within a plastic sack impervious to microorganisms in such fashion that the package is airtight and has as little air space therein as is conveniently possible. The sack material should be proof against the entrance of microorganisms and for this purpose polyvinyl or polyethylene films among others are satisfactory. Also if desired, metal foils or treated It will be appreciated, how-- millimeters thick. This ribbon or band is fed into a beam of high intensity electrons produced by an accelerator of any suitable type, such as that forming the subject matter of U. S. Patent No. 2,429,217, for instance which has the capability of accelerating electrons to a velocity equivalent to two million volts. The apparatus is set up so that the electrons generated bombard the band from opposite faces. For the dimensions given the electrons should be accelerated to a velocity of approximately 2.1 million volts.

This technique and voltage will cause thorough penetration of the material by the electrons without substantial over-irradiation of anyportion of the product. The bombardment treatment is continued until a sterilizing dose of 1.5 times 10 REP has been absorbed. The speed with which the material is continuously fed through the electron beam is adjusted to accomplish this, and depends, of course, upon the irradiating power of the equipment available. Preferably the intensity of the electron beam should be enough so that the sterilizing dose specified above will be absorbed without subjecting any portion of the product to bombardment for more than a few seconds. Under these conditions biological sterility is obtained throughout the meat as well as throughout the packaging material, without bringing about harmful organoleptic changes in the meat substance.

At a convenient time following sterilization, the ribbon of packaged meat is squeezed together so as to separate the meat at regular intervals by bands which extend transversely of the strip. This provides continuous areas of the packaging material which is brought together from opposite sides into face to face relationship along bands extending transverely of the ribbon. The film at these areas is then lheatesealed together. The meat-within=the longitubeiis therefore isolated intoaindividual packages connected: in series by i the heat :sealed itransverse bands. The tube is then cut-into vindividual,pieces along the center lines of these th eat-sealed bands -so as to 'form hermetically sealed. individual .packages which may, 1' for instance, weigh one pound net each.

Theseindividual packages are then enclosed in permaneat-storage containers. For instance cardboard with or without transparent Windows may be used. If rough handling or: prolonged storagepcriods are expectedrthe material may be packedlintoia more rugged outer container madel'ofwood,rigid-plastic or. metal for instance.

all itis desired to store the: raw ground meat form indefinitely longlperiod it is advantageous ifthe outer container is also hermetically sealed so as to, prevent the'slow change in humidity of the meat product which may take place tthrough the cellophane wall. Preferably under these conditions the wall surfaceiof the outer'hermeticah lysealed container and the space between the inner wall of the outer container and the outer wallof-the cellophane wrapped package should be sterilized and this may be accomplished in easy fashion for instance by exposing the final packaged product to a dose of high intensity electrons having a range sufficient to penetrate the outer package and the space about the inner package but not suflicientto penetrate appreciably into the meat.

Meat or other products so packed can be stored in the raw, cooked, or partially cookedstate, at room temperature for indefinite periods so long as the hermetic sea of the inner wrapper is not broken.

The salient feature'of theinvention is that the food substance is treated in thin section which can be adequately sterilized with relatively low velocity electrons and that this thin sectiongof the food'substance is enclosed within a deformable, airtight container which is proof against the passage of microorganisms. treatment container, any air, gas ormoisture which may be within the container, and the food substance itself are all sterilized simultaneously. Recontarnination of the food substance after sterilization is impossible since it is enclosed within theimpervious envelope and, under these conditions, although theproduct eventually is to reachthe market within a tin can or other protective container; it is not necessary. to sterilize the interior of the' exterior container.

The process maybe varied by using films which. are

under sterile conditions, or if desired, after-radiation sterilization, pliable packages such as these can simply be sealed in cans which are subsequently lightly-bombarded The result is that the.

'4 so as to sterilize the can, the air orother gas therein and the surface of the pliable package.

One of the great advantages of this process is that it makes it feasible to sterilize comparatively large individual packages of foods by the .use of electron accelerating equipment of only five million volts capacity or even less. The, process thus avoids the: necessity for operating equipment at extremely high voltages in order to obtain penetration to the center of containers of ordinary size. This is important, since it involves greater 'difiiculties and is far more costly to obtain deep penetration by sterilizing electrons than it is to obtain broad electron beams. For many products-at least this process will result in the ultimatepackaged sterileproduct being provided at less cost than would be involved if the substance were first packaged in the sheet metal can and subsequently sterilized by high voltage electrons having the necessary penetrating range to insure sterility of *all the product.

Another advantage is'that there=is danger thatsmall amounts of radioactive isotopes will beforrned-in food substances if .deep penetration is=attempted throughthe use of electrons accelerated to over tenmillion electron volts-.for instance. This danger is completely avoided by the present process.

Having described our invention, what we claim asnew and useful. and desire to secure'by Letters Patent of the United States, is:

The process for producing a sterile package of ground meat by theme of 'an electron accelerator having a capability of accelerating electrons to a velocityequivalentito substantially two rnillion'volts, which comprises providing-a quantity of the ground meat, sealing said quantity into a pliable container'forrned of amaterial which is impervious to-the passage ofmicroorganisms, flattening the filled ground meat package thus-formed-so that no portionthereof is more than substantiallytwelve millimeters thick, subjecting the flat packagethus formed to bombardment for a few seconds from said accelerator on both faces thereof to adose of approximately 1. 5 times 10 REP sons to sterilize the groundmeat,reshaping the packagelto more convenient form for handling, and enclosing the pliablepackage as thus reshaped in a second container more resistant todeformation than said pliablepackage.

References Cited in the file of this patent UNITED STATES'PATENTS Re. 23,195 Brasch Feb. 7, 1950 2,347,640 Peters May 2, 1944 2,456,909 Brasch Decrll, 194

QTHER REFERENCES Chemical and Engineering News, July 9, 1951, page 2818, article entitled Cathode Rays Recommended for Food, Drug sterilizing. 

